Scholars Day Archive

Scholars Day: April 7, 2010

Foraging Behavior of Nocturnal Rodents is Influenced by Both Direct and Indirect Cues of Predation Risk

Predation risk cues can influence prey foraging decisions, resulting in reduced energy intake in the presence of high-risk cues; yet diet selectivity for different food types while experiencing these cues is less well understood. The presenter investigated the influence of direct and indirect cues of predation risk on seed type selectivity of nocturnal rodents, using black oil and striped sunflower seeds. Predator urine and lack of vertical cover were used as direct and indirect cues of predation risk, respectively. Foraging choices were evaluated based on giving-up densities (GUDs), the amount of food remaining in feeding trays. Microhabitat cover was an important factor in influencing GUDs during both odor-free and predator-odor treatments. Rodents consumed more black oil than striped sunflower seeds, regardless of microhabitat cover and olfactory cues. They did not respond to coyote urine, but their foraging activity in open trays changed when mink urine was added; they not only decreased the total amount of seeds consumed but also became more selective, consuming a greater proportion of black oil sunflower seeds. This suggests that mink were perceived as a greater threat than coyotes. There was a time lag in the prey response to the removal of mink urine from foraging stations; this could be due to residual odor or site assessment and association by the rodents. This finding highlights the importance of taking lag effect into consideration when designing foraging experiments. Lastly, the presenter found that rodents carried seeds from open trays and consumed them in covered trays. Since food items were not eaten at the patches where they were encountered, GUDs may be unreliable as quantitative measures of foraging behavior, suggesting that they should not be used to directly estimate energetic or metabolic losses.